A process of the above noted type is described in German Pat. No. 2 339 591. Instead of the form of treatment of waste-paper which has normally been used in a pulper, which has known disadvantages, in the process described in this specification, the waste-paper is pulped substantially by a purely chemical process. The bales of paper are broken up in a shredder and are then introduced via a feed screw into a reaction tower in which the pulping process is carried out with stock densities of more than 10%, and in the presence of chemicals. Separation of foreign matter present in the waste-paper is carried out after the paper has been pulped in the reaction tower, by means of cyclone separators, vibration sorters, and the like.
However, foreign matter which may become entangled, such as wires or twine, for example, present problems. These may wind themselves round the rotating parts such as the shredders, the thread on the screw conveyor, or the propeller rotor or agitator in the reaction tower, for instance. This interrupts the treatment process and sometimes also damages the rotating parts.